A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Present trends in lithography tend towards an increase in throughput (i.e. an increase in the number of wafers to be processed per time unit) and an increase in resolution of the pattern, i.e. a decrease in the dimensions of the patterns to be provided onto the substrate. These requirements translate into an increase in scanning velocities of e.g. the substrate table that supports the substrate, as well as in an increase in accuracy, e.g. of the positioning of the substrate table, patterning device, etc. Such increase in speed may require a use of relatively lightweight stages (such as a substrate stage or a mask stage). Given the high velocities and corresponding accelerations such lightweight structures may evoke resonances, in other words not behave as rigid body masses. To be able to cope with such non rigid body behavior, multiple position sensing has been proposed so as to obtain over-determined position sensing information to thereby enable to sense non rigid body behavior of a part, such as a substrate table, patterning device support etc. Data obtained about the non rigid body behavior, such as about resonances, bending, expansion, etc, may be applied in actuator control systems so as to compensate for and/or counteract such behavior.